--> ABSTRACT: Mechanisms for Tectonic Erosion of an Accretionary Complex in the d'Entrecasteaux Zone-New Hebrides Island Arc Collision Zone, by J. Y. Collot, M. A. Fisher; #90097 (1990).

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ABSTRACT: Mechanisms for Tectonic Erosion of an Accretionary Complex in the d'Entrecasteaux Zone-New Hebrides Island Arc Collision Zone

J. Y. Collot, M. A. Fisher

In the southwest Pacific Ocean the d'Entrecasteaux Zone (DEZ) is an arcuate submarine mountain chain that collides with the central part of the New Hebrides island arc. The collision zone moves slowly (2.5 cm/yr) northward along the trench, owing to the small oblique angle between the DEZ and the azimuth of convergence. Extensive Seabeam bathymetry as well as single- and multichannel seismic reflection data were collected over both the collision zone and the accretionary wedge that lies south of this zone. These data indicate that the accretionary complex underwent considerable tectonic erosion in response to oblique subduction of the DEZ during the past 8 Ma. Simplified calculation indicates that the mean erosional rate of this complex is 800-900 km3/Ma.

The main mechanisms for tectonic erosion of the accretionary complex involve mass wasting and extensional tectonics. First, mobilization and mass wasting of accreted rocks result in overlapping slump masses that blanket the arc slope. Second, block sliding along an extensional detachment within accreted rocks strips off the upper (about 1 km) part of the accretionary complex. Third, as the DEZ moves northward, the accreted rocks in the wake of the DEZ lose support and collapse along large normal faults that trend oblique to the arc slope. An additional errosive mechanism involves the formation of a deep subcircular reentrant into the accretionary complex; the reentrant is believed to be a scar caused by the collision and subduction of a seamount. The reentrant cuts downward through th accreted rocks almost to the depth of the abyssal oceanic plain.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990